1. Field of the Invention
The invention relates to an integrated inkjet print head and the manufacturing process thereof.
2. Discussion of the Related Art
As is known, inkjet print heads based on different technologies and with different print qualities and speeds, as well as costs, are currently available on the market.
The most widespread technologies are based on thermal and piezoelectric methods. Thermal print heads have one or more xe2x80x9cmini-gunsxe2x80x9d including an ink chamber connected to an ink ejection nozzle and having a heater element located on the base of the ink chamber and formed by a resistor. A very small quantity of ink (of the order of picoliters), present in the ink chamber, is heated quickly by the heater element; boiling generates a bubble which, on collapsing, causes the ink to come out of the nozzle. The change of pressure which takes place inside the chamber draws from the reservoir, connected to the ink chamber by means of a suitable duct, another small quantity of ink which can again be heated and projected to the outside. With this method the frequency with which the drops can be expelled thus depends on the heating time and the re-charging speed.
The piezoelectric method makes use of the property of a number of materials, such as quartz, to contract if subjected to electric field. This behavior is exploited to generate a pressure on a capillary containing ink. The pressurized liquid comes out of the nozzle located in the direction of the support to be printed. In this case the frequency with which the drops of ink can be generated by the nozzle depends on the physical characteristics of the vibrating component, and on the recharging time of the capillary.
For a rapid survey of the two methods discussed above, reference may be made, for example, to U.S. Pat. No. 4,543,530 which also shows the structure of a thermal-type head, and the article xe2x80x9cInkjet: tecnologie a confrontoxe2x80x9d (xe2x80x9cInkjet: technologies comparedxe2x80x9d) in PC MAGAZINE, April 95, pp. 200-210. Furthermore, another structure of a thermal-type head is shown in U.S. Pat. No. 5,103,246.
In both methods, the shape of the drop of ink ejected is of fundamental importance. In fact, the more spherical the drop, the better the print quality. To obtain this result it is necessary to act so that the ink is subjected to a change in pressure which is as violent and at the same time as short as possible. The method which enables this shape to be obtained most satisfactorily and most easily is the thermal method. To induce a rapid change in pressure the heater element is caused, by Joule effect, to generate heat such as to cause a temperature change in the ink of 100xc2x0 C./xcexcs. The nucleation of the bubble requires approx. 3 xcexcs while its growth involves times of 3-10 xcexcs; collapse involves times of 10-20 xcexcs, while the re-charging of the ink requires approximately 80 xcexcs.
It is evident that the times, temperatures and pressures involved induce considerable stress in the heater elements, reducing their average lifetime. It is therefore desirable to devise arrangements capable of reducing the stress to which the heater element is subjected. In particular, it is conceivable to calibrate the minimum energy to be supplied to the heater element, by means of a sequence of xe2x80x9cshotsxe2x80x9d or emissions of the drops.
Furthermore, to avoid damage to the head and its components and to indicate the need to replace them, in these heads it is also important to check whether the emission nozzle is blocked or whether any part of the head, such as the heater element, is damaged.
The object of the invention is therefore to improve an inkjet print head in order to eliminate the above-mentioned disadvantages.
The invention provides an integrated inkjet printhead and a manufacturing process therefore.
According to one embodiment of the invention, an inkjet printhead is provided including an integrated device emitting ink drops and formed by an ink chamber and by a nozzle in communication with the ink chamber, including a drop emission sensor arranged in a position adjacent to the ink chamber.
According to another embodiment of the invention, a process is provided for manufacturing an inkjet printhead, including the steps of forming an ink chamber and a nozzle in communication with said ink chamber, and forming a drop emission sensor in a position adjacent to said ink chamber.
In practice, the invention is based on the knowledge that at the moment of emission of a drop of ink, in a direction perpendicular to the silicon chip, by virtue of momentum conservation the latter is subjected to a recoil movement. Thus, by arranging a movement sensor in the proximity of the ink chamber or of each ink chamber of the head it is possible to detect the emission of the drops of ink in real time. In view of the fact that this movement causes a change in the pressure exerted on the mini-gun support structure, advantageously this movement may be noted by detecting differences in the pressure exerted on that structure. In particular, it is possible to arrange a resistive element on the wall of the ink chamber opposite the ink emission nozzle, the resistor having a resistance variable as a function of the pressure exerted on it. A suitable circuit connected to this resistive element and capable of detecting its changes of resistance thus enables one to identify whether and when a drop of ink is emitted. The resistive element may be made of single-crystal silicon, integrated into the substrate, or of multi-crystal silicon, on top of the wafer and beneath the heater element. Advantageously the sensor may be integrated together with the components of the circuitry for the control and detection of the emission of the drops of ink, using the usual known monolithic manufacturing methods.